Motor control system



March 12, 1957 R. R. BAKER MOTOR CONTROL SYSTEM Fil ed Aug. 20, 1954 INVENTOR Rest R. Baker WITNESSES T ix d l u ATTORNEY MOTOR CONTROL SYSTEM Application August 20, 1954, Serial No. 451,119

5 Claims. (Cl. 318-76) This invention relates generally to motor control systems and more particularly to systems for maintaining predetermined speed relationships or ratios between a pair of motors or between one motor and several motors controlled in dependence of operation of said one motor.

Arrangements of this general nature are employed, by way of example, in rotary paper cutter or knife drives. In such a drive a pull roll stand pulls the paper Web from one or more reels and feeds the paper web to one or more rotating knives. In some instances a slitter cutter may be disposed between the pull roll stand and the rotating knives to slit the paper web into strips of desired width. The rotating knives cut the paper web into suitable lengths, forming sheets which are thereafter automatically stacked.

The knife roll comprises simply a long knife which is radially mounted on the periphery of a roll so that its cutting edge extends approximately longitudinally of the knife roll assembly. The knife cooperates with an anvil over which the paper web passes so that each time the knife passes the anvil it cuts the paper web therebetween. By changing the ratio between the speed of the knife roll and the pull roll assembly, the paper web may be cut into sheets of any desired length within the adjusting limits of the roll speeds. The accuracy of performance in determining the length of cut of the paper web with each revolution will depend on the accuracy with which the speed ratio is maintained between the knife roll and the pull roll.

In order to avoid excessive waste of material in subsequent squaring and trimming operations, if used, it is essential that the sheets be cut into lengths which are uniform within very close limits. This typeof equipment may be supplied with a single knife roll or it may include two or more knife rolls. When two or more knife rolls are used the sheet is usually slit along its length and the individual slit web sections are then passed under the respective rotating knife assemblies.

In drives of this type the speed range varies considerably. During the threading operation, that is during threading of the paper web from the reels, through the pull rolls, through the slitter and through the knife rolls, the machine is operated at slow speed. With the com pletion of the threading operation, the machine is accelerated to a suitable operating speed which may be of the order of 8 to 10 times the threading speed or higher. It is also customary practice to operate the cutters or knives over a productive speed range so that sheets cut to various lengths may be properly handled, that is the time required to handle a sheet which is short in length is usually less than that required to handle a sheet of longer length. Consequently, speed adjustment of the knife roll assembly to take care of this condition is needed. It is also necessary to adjust the length of cut and this is accomplished by varying the ratio between the speed of the pull roll assembly and the speed of the knife roll. I

ited States Patent 0 Conventional practice has been to drive the rotary cutters or knives with a single input shaft. Power is transmitted from this shaft to the pull roll stand through a gear train or other suitable mechanical connection. Power is also transmitted from the input shaft to each of the knife rolls through a speed changer and another gear train or equivalent mechanical drive. All of these mechanical parts connected between the input shaft and the knife rolls must be of adequate capacity for driving these rolls and the speed changer must provide sufficient speed adjustment to cover the range of sheet lengths which are required. With this conventional arrangement it will be appreciated that each speed changer is required to transmit the full operating load of the knife roll. Due to the nature of the cutting operation, the knife roll undergoes extreme load variation, impact existing at each contact of the knife edge with the paper web. Such pulsating loads subject all the component parts to heavy stresses. Consequently, the wear is rapid. Operation of the knives with the conventional type of drive discussed usually results in excessive power losses and poor accuracy in maintaining constant sheet lengths. All this is the result of the wear of the equipment.

Accordingly, one object of this invention is to provide a rotary paper cutter drive which is accurate and durable.

More specifically stated, it is an object of this invention to provide a drive for a rotary paper cutter machine in which mechanical connections between the several stands are eliminated.

In a broader sense, it is an object of this invention to provide an arrangement for synchronizing the operation of one motor with another.

In connection with the preceding object, it is an object of this invention to provide an electric drive in which one motor is synchronized with another wherein provision is made for synchronizing motor operation over a wide range of speed adjustments and which will maintain a preselected synchronizing adjustment within close limits.

'It is also an object of this invention to provide a control wherein one or more motors are synchronized with a single motor.

Further to the preceding object, it is an object hereof to provide synchronization of one or more motors with a given motor over a wide range of operating speeds and speed ratios.

Yet another object or" this invention is to provide an electric drive of the character referred to wherein different speed ratios between several synchronized motors and a main motor may be selected.

The foregoing statements are merely illtustrative of the various aims and objects of this invention. objects and advantages will become apparent from a study of the following specification when considered in con junction with the accompanying drawing in which the single figure thereof illustrates a variable voltage drive embodying the principles of this invention.

The drawing illustrates this invention in connection with a rotary paper cutter drive. This is merely exemplary of one of the numerous applications of this invention. The apparatus involves an unwind stand, the details of which are not shown in the interest of simplicity, on which one or more reels of paper are supported. The reels herein illustrated are numbered 1 and 2. The paper webs from reels 1 and 2 are fed to a pull roll stand, generally designated 4, which comprises a driven roll 5 and a pressure roll 6. As illustrated herein, the paper web from reel 1 is fed through the pull rolls on top of the paper web from reel 2. This is one method of operating the arrangement. The contact or nip pressure of. the rolls of the pull stand with the paper web therebetween is sufficient to avoid slippage for the operating conditions.

The paper web may be fed from the pull roll stand through a slitter cutter comprising a bearing roll 8 and a circular knife 1% which slits the paper web in this instance into two strips of predetermined width. The respective webs resulting from this slitting operation then pass to respective rotary cutters generally designated 12 and'14. Rotary cutter 12 comprises a rotating knife 16 and a cooperating anvil 17 and rotary cutter 14 comprises a rotating knife -3 and cooperating anvil 19. At this point the paper web is cut into suitable lengths as indicated by the r spective sheet groups 29 and 21 on the output side of the cutters. Sheet groups 2'3 and 21, in practice, drop on a conveyor be t arrangement which carry the cut sheets to a suitable stacking stand. It will be appreciated from this discussion of equipment that accurate maintenance of the ratio of the angular speed of the rotary cutters to the angular speed of the pull roll 5 is essential if the paper web is to be cut into sheet groups of uniform length.

The electric drive diagrammatically illustrated herein accomplishes this end and comprises a pull roll motor generally designated PM which is mechanically connected to pull roll 5 by any suitable means to drive the pull roll. The rotating knives are driven by direct current knife motors KMi and KM2 suitably mechanically connected to respective knife rolls 16 and 18. The pull roll motor 1 M and the knife motors KM1 and KMZ are energized in parallel by a direct current generator, generally designated MG. Direct current generator MG is driven at constant speed by any suitable means such as an alternating current induction motor DM which functions as the drive motor for the motor generator set. Main generator MG is provided with a field winding MGF, the excitation of which is controlled by means of a field rheostat PR3 which is connected to a suitable supply of direct current, the adjustable tap of the field rheostat determining the degree of excitation of the field and, hence, the output voltage of this main generator.

Adjustment of the field rheostat PR3 varies the output voltage of the main generator MG which correspondingly varies the armature terminal voltage of each of the pull roll motors and the two knife roll motors. This type of variable voltage drive is well known in the art and provides a range of motor speed control which is of the order of about to 1 or more.

Further speed control of each of the knife roll motors is obtained by means of the respective field windings F1 and F2 for these motors. The excitation of field winding F1 is controlled by means of a field rheostat FRI and the excitation of field winding F2 is controlled by means of a field rheostat PR2. The speed of each knife motor is regulated by respective booster generators BGI and BGZ, the armature circuits of which are connected in series with the respective knife motors. These generators are provided with field windings respectively designated BF1 and BFZ which are controlled by respective magnetic amplifiers MA1 and MA2, in turn controlled by respective differential regulators, generally designated DR1 and DR2.

Each of the knife motors KM1 and KM2, by means 'of the respective differential regulators and the respective booster generators, is synchronized in predetermined speed ratio with the pull roll motor PM. This is accomplished in the case of knife motor KM1 by means of a mechanical differential, generally designated D1, having a pair of input shafts D11 and D12. Shaft D11 is mechanically connected to knife motor KMI to be driven thereby, while shaft D12 is driven through a synchrotie transmission system involving a synchrotie transmitter ST1 driven at some selected speed by the pull roll motor through an adjustable speed changer SC1. The electrical output of the synchrotie transmitter 8T1 is applied to a synchrotie receiver SR1, the rotor element of which is connected to the differential input shaft D12. The cage element of this differential is designated CA1 and is connected to operate any suitable type of electrical pickofi" such as the adjustable control rheostat CR1, the tap of which is connected to the cage element CA1. The requirement here is that the pickoff shall load the mechanical differential as lightly as possible so that the load placed upon the synchrotie receiver SR1 will be of a minimum value so that its angular position at any instant will closely correspond to the angular position of the rotor of the syn chrotie transmitter ST1.

The magnetic amplifier illustrated herein is shown in its simplest form as a matter of convenience. It is provided with a magnetizable core, a main Winding M1, a bias winding B1 and a control winding C1. The main winding M1 is adapted for energization with alternating current and includes in its circuit a self-saturating rectifier SR1 and booster generator field winding BF1. The bias winding of this magnetic amplifier is energized with direct current and in one method of operating this system it is adjusted to bias the magnetic amplifier to a given point, for example, approximately to the midpoint of its outputcharacteristic when the ampere turns of the control winding C1 are a value corresponding to zero error in synchronization between the knife motor KMl and the pull roll motor PM. The control winding C1 of this magnetic amplifier is also energized with direct current and its ampere turns are controlled by the series connected control rheostat CR1 which constitutes the electrical pickoff of the mechanical differential D1. At zero error, by Way of example, the tap of this control rheostat may occupy a position adjacent its midpoint. The ampere turns of bias winding B1 are differentially related to the ampere turns of control winding C1. The magnetic flux produced by the bias winding B1 is in opposition to the magnetic flux produced by the main winding M1 on the conducting half cycles of the main winding as determined by the self-saturating rectifier SR1 and, as described, may bias the magnetic amplifier to approximately the midpoint of the more linear portion of its output characteristic in the presence of the zero error dilferential ampere turns of the control winding C1. The ampere turns of control winding C1 therefore produce a'magnetic flux in the amplifier core in the same direction as the magnetic flux produced by the main Winding M1. Thus when the ampere turns of the control winding C1 increase, the core is driven further into saturation and the output of the main winding M1 correspondingly increases due to the drop in impedance. Conversely,

'when the ampere turns of the control winding C1 decrease, the bias ampere turns predominate to a greater extent and the core is driven further from a condition of magnetic saturation. Consequently, the impedance of the main winding M1 increases and its output decreases. In this manner the excitation of the booster generator field winding BF1 is varied to increase or decrease the booster generator output in the system and, consequently, vary the control of knife motor KM1 to vary its speed as required.

When the knife motor KMl is operating at a speed such that the speed ratio between it and the pull roll motor PM is that selected at the speed changer 8C1, the difierential speeds between the differential input shafts D11 and D12 will be zero. Consequently, there will be no rotation of the differential cage CA1 and the tap of the control rheostat CR1 will be positioned so as to maintain the knife motor speed at its proper value. Any tendency for speed excursions of the knife motor KM1 from that which is selected results in a differential speed across the differential which is sensed by the cage element causing its rotation to correspondingly vary the position of the tap of control rheostat CR1. This change in tap position at the control rheostat changes the control of the magnetic amplifier MAI in such sense as to correct the speed error to closely lock the speed of the knife roll 16 to the selected speed to maintain accurate sheet lengths.

The arrangement described to this point functions essentially as a position regulator. However, such systems are inherently diificult to stabilize in view of the large amount of power which is required to keep the;

synchronized motor in step with the synchronizing motor. Provision is therefore made herein for synchronizing the pull roll motor and the knife roll motor KMl as to speed, in one sense through the variable voltage armature control afforded by the parallel connection of the motors with the main generator to receive simultaneous variations in armature voltage with adjustment of field rheostat PR3, and, in a second case, by means of the control afforded by knife motor KMI through adjustment of its field rheostat PR1.

Specifically, this adjustment of the tap of the field rheostat is accomplished by the adjusting means 24 of the speed changer SCI. When this adjusting means is moved to change the drive ratio between the pull roll motor PM and the knife motor KMl the tap of field rheostat PR1 is correspondingly adjusted to change the excitation of the field P1 of the knife roll motor. This changes the base speed of the knife roll motor and thereby considerably minimizes the burden which is placed upon the position regulator in synchronizing the knife roll motor with the pull roll motor, because it is measurably easier to synchronize one motor with another as to instant angular position when said one motor is operating essentially at the required speed.

The control of knife roll motor KM2 is similar to that discussed in connection with knife roll motor KM1. In this case the tap of field rheostat PR2 is controlled by the speed adjusting means 26 of the speed changer 8C2. Magnetic amplifier MA2 comprises a main winding M2, 8. self-saturating rectifier SR2 and the main winding circuit includes in series therein the field BF2 of booster generator BGZ and is energized with alternating current. Bias winding B2 and control winding C2 are again differentially related and their combined ampere turns under quiescent conditions bias magnetic amplifier MA2 approximately to the midpoint of its linear characteristic. The ampere turns of control winding C2 are controlled by a control rheostat CR2 energized with direct current and the tap of this control rheostat is controlled by the cage element CA2 of differential D2, the input shaft D21 of which is driven by knife motor KM2 and the other input shaft D22 of which is driven by a synchrotie receiver SR2 in turn controlled by a synchrotie transmitter S2 driven by speed changer 3C2 from the pull roll motor PM. The function of this part of the system is the same as that described in connection with knife roll motor KM1.

The magnetic amplifier circuits, asnoted hereinabove, are illustrated in simplified form merely for the purpose of demonstrating the control principles which are involved. In actual practice, if magnetic amplifiers are employed, full wave magnetic amplifier circuits offer a better arrangement, or, alternatively, respective arrangements of parallel connected doubler type magnetic amplifiers each feeding a full-wave load rectifier having its output terminals connected to one booster generator field winding would be utilized. Such expedients are conventional and are not believed to require illustration. Additionally, it is standard practice in such magnetic amplifier controls, or for that matter in any type of closed loop regulator control, to provide suitable feedback of the derivative type in order to obtain the required degree of system damping to achieve system stability. Further, it is believed clearly understood that other types of amplifiers such as the rotating type may be utilized in place of the arrangement herein considered.

It will also be appreciated that the use of control rheostats such as CR1 and CR2 are merely illustrative of a way of obtaining an electrical signal in dependence of differential cage movement. There are numerous varieties of pickups available for such an arrangement including the resistive type illustrated, capacitive types and various inductive types. Additionally, the circuit configuration illustrated may be varied to include electrically balanced arrangements which for a given position of the tap may have zero electrical output resulting in zero ampere turns at the control winding C1. With such arrangements if it is desired to bias the amplifier to the midpoint of its output characteristic the bias ampere turns could be selected to provide such control independently. Still further, while mechanical differentials and the electrical motion transmitting arrangement represented in the synchrotie systems provide a convenient and durable way of measuring speed differentials between the pull roll motor and the respective knife motors, it will be appreciated that conventional electrical expedients may be utilized in place of this arrangement.

Therefore, although but one embodiment of this invention has been illustrated herein, it will be appreciated by those skilled in the art that this invention, both in its details and in the organization of such details, may be subjected to considerable variation without departing from the spirit and scope thereof. Accordingly, it is intended that the foregoing disclosure and the showing made in the drawing shall be considered only as illustrative of the principles of this invention and not construed in a limiting sense.

I claim as my invention:

1. A motor speed control comprising, a main motor, a controlled motor, a booster generator connected in series with said controlled motor, means for energizing said main motor in parallel with said series connected controlled motor and booster generator, a field Winding on said main motor, a field winding on said controlled motor, a field winding on said booster generator, means responsive to speed differentials between said main motor and said controlled motor for controlling the excitation of said field Winding on said booster generator, adjustable means for varying the speed ratio between said main motor and said controlled motor, field excitation control means connected to control excitation of the field winding of said controlled motor, and means responsive to adjustment of said adjustable means for controlling said field excitation control means.

2. A motor speed control comprising, a main motor, a controlled motor, a booster generator connected in series with said controlled motor, means for energizing said main motor in parallel with said series connected controlled motor and booster generator, a field winding on said main motor, a field winding on said controlled motor, a field winding on said booster generator, means responsive to speed differentials between said main motor and said controlled motor for controlling the excitation of said field winding on said booster generator, adjustable means for varying the speed ratio between said main motor and said controlled motor, and means responsive to said adjustable means for varying the excitation of said field winding on said controlled motor.

3. A motor speed control comprising, a main motor having a field winding, a controlled motor having a field winding, a booster generator connected in series with said controlled motor and having a field winding, means for energizing said main motor in parallel with said controlled motor and series connected booster generator, an amplifier having an output circuit connected to energize the field winding of said booster generator and having an input circuit, a mechanical differential having a pair of input shafts and an output shaft, a speed changer connecting one of said input shafts to said main motor to be driven thereby, a speed adjusting member on said speed changer, means connecting the other of said input shafts to said controlled motor to be driven thereby, an elec trical device actuated by said output shaft and connected to control said input circuit of said amplifier, and means responsive to movement of said speed adjusting member of said speed changer for controlling the excitation of the field winding of said controlled motor.

4. A motor speed control comprising a main motor having a fiel'd winding, a controlled motor having a field winding, means for energizing both of said motors, variable voltage means having an output circuit connected to control energization of said controlled motor and having an input circuit, differential means responsive to the speed of both of said motors and having an electrical output connected to control said input circuit of said variable voltage means, adjustable means for varying the speed relationship between said main motor and said differential means, field excitation control means connected to control excitation of said field Winding of said controlled motor, and means responsive to adjustment of said adjustable means for controlling said field excitation control means.

5. A motor speed control comprising a main motor having a field winding, a controlled motor having a field winding, means for energizing both of said motors, variable voltage means having an output circuit connected to control energization of said controlled motor and hav- References Cited in the tile of this patent UNITED STATES PATENTS 1,685,960 Schiller Oct. 2, 1928 2,298,877 Edwards et al Oct. 13, 1942 2,427,223 Moore Sept. 9, 1947 2,432,497 Behrens Dec. 16, 1947 2,613,741 Battersby Oct. 14, 1952 2,634,811 Schaelchlin Apr. 14, 1953 

